Activation of trehalase by heat shock in yeast ascospores: Correlation with total cellular cyclic-AMP content

Abstract

A short heat treatment (1 min or 3 min) of yeast ascospores resulted in a tenfold increase in the activity of trehalase as measured in extracts made after the heat shock. The optimal temperature was about 52°–54°C. The heat stability of trehalase in spore extracts was much lower than in the intact spores. When the cyclic-AMP level was measured in the spores during the heat treatment, a steady decrease was found. In these experiments the spore samples were immediately frozen in liquid nitrogen after the heat treatment. However, when the spores were first cooled with a large amount of ice-cold distilled water, as was done for the experiments on trehalase activation, an increase of the cyclic-AMP level was found which was about two-to threefold at the optimal temperature. When the activity of trehalase was measured after heating of the spores followed by rapid freezing in liquid nitrogen, no activation of trehalase was observed. Control experiments showed that trehalase was not destroyed by the freezing procedure. These results demonstrate that both the activation of trehalase and the increase of the cyclic-AMP level occur during the cooling of the spores and not during the heat treatment itself. They suggest possible involvement of cyclic AMP in the heat activation process of trehalase.